This study was conducted, as part of a field-ecology study of arboviral activity in the Amazon Basin of Peru, to determine the taxonomy, frequency, seasonal, and vertical distributions of potential mosquito vectors. In addition, the relative efficiency of human-landing collections and dry ice-baited Centers for Disease Control (CDC)-type light traps was determined for collecting mosquitoes. A total of 70 species of mosquitoes from 14 genera were collected from June 1996 through December 1997 of forested site near Puerto Almendras, 20 km west southwest of Iquitos, Peru. Three species Psorophora (Janthinosoma) albigenu (Peryassu), Ochlerotatus (Ochlerotatus) fulvus (Wiedemann), and Ochlerotatus (Ochlerotatus) serratus (Theobald) accounted for 70% of all mosquitoes captured in human landing collections. Overall, biting activity occurred throughout the 24-h cycle, but was higher during daytime hours, primarily because of large populations of two day-biting species, Ps. albigenu and Oc. serratus. Oc. fulvus was active throughout the 24-h cycle, but was more frequently collected during the evening hours. Oc. fulvus, Ps. albigenu, Culex (Melanoconion) pedroi Sirivanakam & Belkin, and a mixture of Culex (Melanoconion) vomerifer Komp, and Culex (Melanoconion) gnomatos Sallum, Ruchings, & Ferreira, accounted for 73% of the mosquitoes captured during the hours of darkness by human collectors. In general, Ochlerotatus spp. and Psorophora spp. were more commonly captured in human landing collections, whereas most Culex spp. were more frequently collected in the dry ice-baited CDC-type light traps. In general, mosquito populations were lowest from June through August when river levels were at their lowest. Two large population peaks occurred in November-December and in February March as a result of flood-water mosquito populations (e.g., Ps. albigenu).